This proposal will focus on the evaluation of the biochemical properties of the poliovirus polymerase. Poliovirus is the best characterized of the Picornavirus. The extensive knowledge of this system and the availability of vector clones for most of the polio proteins (including the polymerase) makes polio an attractive system to model picornavirus replication. The biochemical properties of the poliovirus polymerase will be evaluated in terms of processivity under different conditions including variations of salt, Mg++, pH, nucleotide concentration and temperature. Determination of other activities that the enzyme may possess such as displacement of nucleic acid strands and duplex-unwinding (helicase) activity will also be tested. it has been show that picornavirus undergo substantial recombination. The capacity of the enzyme to catalyze recombination in vitro will be tested. In addition studies will be conducted to determine the possible effect of cellular factors from uninfected and virus infected cells on RNA synthesis by poliovirus polymerase. An extensive understanding of picornavirus replication could aid in the development of specific therapies targeted against a unique step in viral replication.